1. Field of the Invention
This invention relates to an electrical switch for use in switching to a bypass circuit of a liquid circulation system, such as an hydraulic system or a lubrication system for circulating lubricating oil. More particularly, this invention relates to a pressure differential switch that self-actuates as a result of an excessive pressure differential in a liquid circulation system.
2. Description of the Prior Art
U.S. Pat. No. 4,130,745, to Hetzer, discloses a pressure differential detector switch utilizing a piston which is free to travel within a housing. One side of the piston is exposed to the high pressure side of a pressure differential application, and the other side is exposed to the low pressure side. A spring is provided in the housing to resiliently urge the piston toward the high pressure side, in cooperation with the pressure on the low pressure side. When the force on the piston resulting from pressure differential between the high pressure side and the low pressure side exceeds the force on the piston resulting from the spring, the pressure differential force will move the piston away from the high pressure side to compress the spring. The piston carries a permanent magnet, and a reed switch is positioned on the outside of the housing to be magnetically actuated by the change in position by the travel of the piston that results from an excessive pressure differential condition. A reed switch of the type utilized in the device disclosed in this patent has limited current carrying capacity and a high resonant frequency due to its low moving mass and high spring constant.